Methylmalonic acid cobalamins

Methylmalonic acid (MMA) in semm is an estabUshed marker of cobalamine deficiency. MMA and other short-chain dicarboxyhc acids react with... 

Vitamin B12 Low serum cobalamin (< 150 pmol/L) accompanied by increased serum homocysteine (> 13 Nnol/L), and increased serum (> 0.4 -mol/L) and urine (> 3.6 mmol/mol creatinine) methylmalonic acid... 

In this hereditary disease up to 1 - 2 g of methylmalonic acid per day (compared to a normal of <5 mg/day) is excreted in the urine, and a high level of the compound is present in blood. Two causes of the rare disease are known/ One is the lack of functional vitamin B12-containing coenzyme. This can be a result of a mutation in any one of several different genes involved in the synthesis and transport of the cobalamin coenzyme.6 Cultured fibroblasts from patients with this form of the disease contain a very low level of the vitamin B12 coenzyme (Chapter 16), and addition of excess vitamin B12 to the diet may restore coenzyme synthesis to normal. Among elderly patients a smaller increase in methylmalonic acid excretion is a good indicator of vitamin B12 deficiency. A second form of the disease, which does not respond to vitamin B12, arises from a defect in the methylmalonyl mutase protein. Methylmalonic aciduria is often a very severe disease, frequently resulting in death in infancy. Surprisingly, some children with the condition are healthy and develop normally.3 1... 

Methylmalonyl-CoA mutase is a cobalamin-linked enzyme of mitochondria that catalyzes the isomerization of methylmalonyl-CoA to succinyl-CoA. A reduction of this enzyme due to vitamin B12 deficiency will result in a metabolic block with the urinary excretion of methylmalonic acid, and the measurement of this metabolite has been used to confirm a deficiency of vitamin B12. The test has also been useful in investigating rare abnormalities of this enzyme that result in the excretion of methylmalonic acid in the presence of adequate vitamin B12. Given an oral loading dose of valine or isoleucine will increase the urinary excretion of methylmalonic acid in patients with a vitamin B12 deficiency (G4). However, Chanarin and his colleagues (CIO) found that one-quarter of their patients with pernicious anemia excreted a normal concentration of methylmalonic acid even after a loading dose of valine. Normal subjects excrete up to 15 mg of methylmalonic acid in their urine over a 24-hour period (Cll). 

S-Methylmalonyl-CoA mutase (EC 5.4.99.2) is a deoxyadenoxyladen-osylcobalamin-dependent enzyme of mitochondria required to catalyze the conversion of methylmalonyl-CoA to succinyl-CoA. A decrease in the activity of methylmalonyl-CoA mutase leads to the urinary excretion of large amounts of methylmalonic acid (C22). The biochemical lesion may be at the mutase level due to an abnormality of apoenzyme protein or an inability to elaborate the required coenzyme form of vitamin B12> i.e., adenosyl-cobalamin. In rare cases the abnormality may be due to an inability to convert the d form of methylmalonyl-CoA mutase to the l form as a result of a defective racemase (EC 5.1.99.1) (Kll). In patients, the nature of the abnormality can be determined by tissue culture studies (D13) and by clinical trial, since patients with a defect in adenosylcobalamin production will show clinical improvement when treated with very large doses of vitamin B12 (Mil). 

The initial dose in cobalamin deficiency anaemias, including uncomplicated pernicious anaemia, is hydroxocobalamin 1 mg i.m. every 2-3 days for 5 doses to induce remission and to replenish stores. Maintenance may be 1 mg every 3 months higher doses will not find binding sites and will be eliminated in the urine. Higher doses are justified during renal or peritoneal dialysis where hydroxy-cobalamin clearance is increased, and resultant raised plasma methylmalonic acid and homocysteine represent an independent risk factor for vascular events in these patients (see later). 

Klee GG. Cobalamin and folate evaluation measurement of methylmalonic acid and homocysteine vs vitamin B12 and folate. Clin Chem 2000 46 1277-83. 

Savage DG, Lindenbaum J, Stabler SP, Allen RH. Sensitivity of serum methylmalonic acid and total homocysteine determinations for diagnosing cobalamin and folate deficiencies. Am J Med 1994 96 239-46. 

Stabler SP, Marcell PD, Podell ER, Allen RH, Linden-baum J. Assay of methylmalonic acid in the serum of patients with cobalamin deficiency using capillary gas chromatography-mass spectrometry. J Clin Invest 1986 77 1606-12. 

Since the coenzyme from vitamin is required in two distinct enzyme reactions, i.e., remethylation of homocystine and catabolism of methylmalonic acid, the fundamental defect must involve a step in converting to its coenzymes. Formation of both deoxyadenosyl B and methyl B requires a prior reductive step catalyzed by cobalamin reductase, which appears to be the defective enzyme in this variant (Hogervorst et al., 2002) (Fig. 20.4). 

The term phenocopy refers to an environmentally induced variation that closely resembles a genetically determined variation. For example, dietary vitamin B deficiency is a phenocopy of the inherited disorder, methylmalonic acidemia and homocystinuria due to cobalamin C disease. Both dietary vitamin B,2 deficiency and cobalamin C disease have the biochemical findings of elevated plasma methylmalonic acid and homocysteine levels. Awareness of phenocopies is important as they provide an alternative explanation for clinical findings. For example, in the case of elevated... 

Some forms of MMA may be responsive to vitamin Bjj. Responsiveness can be determined by administration of 1.0 mg hydroxocobalamin (IM or IV) for 5 days. A reduction in serum methylmalonic acid concentrations of 50 % or greater suggests responsiveness [14]. For those with cobalamin-responsive forms of MMA, intramuscular (IM) hydroxocobalamin injections of 1.0-2.0 mg are often administered daily. A decreased frequency of IM injections or use of oral supplements may be appropriate for older individuals. The hydroxocobalamin form rather than the standard cyanocobalamin form must be used [15]. 

Major vitamin Bi2-dependent metabolic processes include the formation of methionine from homocysteine, and the formation of succinyl coenzyme A from methylmalonyl coenzyme A. Thus, apart from directly determining vitamin B12 concentration in serum, elevated levels of both methylmalonic acid and homocysteine may indicate a vitamin B12 deficiency. Serum cobalamine concentration is often determined by automated immunoassays using an intrinsic factor as binding agent. These assays have mainly replaced the microbiological methods. Literature data about vitamin B12 concentration in serum varies. Values <110-150pmoll are considered to reflect deficiency, whereas values >150-200pmoll represents an adequate status. 

Methylmalonyl-CoA mutase (EC 5.4.99.2). Failure to convert (/ )-methylmalonyl-CoA into succinyl-CoA. Large quantities of methylmalonic acid appear in plasma and urine. Affected children fail to thrive and show pronounced ketoacidosis. Often fatal in early life. Hyperammonemia and intermittent hyperglycinemia are also typical. Restricted protein intake and synthetic diets are helpful, in particular low intakes of leucine, isoleucine, valine, threonine and methionine. A similar condition may arise from a congenital deficiency of methylmalonyl-CoA epimerase (EC 5.1.99.1). Both conditions unresponsive to vitamin Bj2. Another type of methylmalonyl aciduria is thought to result from an hereditary deficiency of deoxyadenosyl transferase (transfers the 5 -deoxyade-nosyl group in cobalamin synthesis), which provides the coenzyme of methylmalonyl-CoA mutase. This condition responds to injection of B,2. Dietary B12 deficiency also results in methylmalonic aciduria. 

Since concentration measurements in blood may not reflect true vitamin status, the measurement of metabolites or activity of enzymes that use a coenzyme form of a B vitamin has been suggested. For example, the measurement of either homocysteine or methylmalonic acid has been suggested as a marker for cobalamin status, and the erythrocyte transaminase coefficient has been suggested as a marker for vitamin Bg status. However, there are no accepted definitions for the diagnosis of vitamin deficiency in the case of many vitamins. 

In humans, cobalamins are essential coenzymes for two cellular enzymes. One is the mitochondrial enzyme, methyl malonyl-coA-mutase, which converts methylmalonic acid (MMA) to succinyl-CoA. The other is the cytoplasmic methionine syntase, which converts homocysteine (Hey) to methionine (reviewed by Banerjee 2006). An insufficient amount of cobalamin in the cells, therefore, leads to increase levels of MMA and total homocysteine (tHcy). 

Valente, E., Scott, J.M., Ueland, P.M., Cunningham, C., Casey, M., and Molloy, A.M., 2011. Diagnostic accuracy of holotranscobalamin, methylmalonic acid, serum cobalamin, and other indicators of tissue vitamin B12 status in the elderly. Clinical Chemistry. 57 856-863. 

Refsum, H., Yajnik, C.S., Gadkari, M., Schneede, J., Vollset, S.E., Orning, L., Guttormsen, A.B., Joglekar, A., Sayyad, M.G., Ulvik, A., and Ueland, P.M., 2001. Hyperhomocysteinemia and elevated methylmalonic acid indicate a high prevalence of cobalamin deficiency in Asian Indians. The American Journal of Clinical Nutrition. 74(2) 233-241. 

Figure 7.3. Scheme of the enzymatic synthesis of cobamides in the cell. AdoCbl and MeCbl are formed from the common precursor OHCbl via two reductive steps catalyzed by separate enzymes. Metabolic disorders due to enzyme defects may occur at the two reductions and additions of adenosyl or methyl residues. High urinary levels of methylmalonic acid (methylmalonic aciduria) indicate an impaired synthesis of AdoCbl, whereas high levels of urinary homocysteine (homocystinuria) indicate an impaired MeCbl synthesis. In patients with high urinary levels of both methylmalonic acid and homocysteine a defective reduction of cobalamin is likely (Rosenberg, 1983). 

Rollman N and Sjostrom G (1946) The behavior of some propionic acid bacteria strains against NaCl, NaN03, and heating. Svenska Mejerit 38(19) 199-201 (20) 209-212 Romanskaya NN, Diment GS and Vorobjeva LI (1985) Method of production of dairy beverages. Avt svidet No 1184506 Bull No 38 Rosenberg LE (1983) Disorders of propionate, methylmalonate and cobalamin metabolism. 

Although cobalt ions are found in both the (II) and (III) oxidation states, the most important biological compound of cobalt is vitamin B12 or cobalamin where the Co(III) form is present (256) (Fig. 6.10). Cobalamin or related substances are important biological compounds that are involved in a great variety of activities, particularly in bacteria. Vitamin B12 is also necessary in the nutrition of humans and probably of most animal and plant species. It is of critical importance in the reactions by which residues from carbohydrates, fats and proteins, are used to produce energy in living cells. Pernicious anemia is a severe disease in elderly people. This disease is usually accompanied in mammals by the increased excretion of methylmalonic acid in the urine. Today it is effectively controlled by a 100 /ig injection of vitamin B,2. 

Type II Methylmalonic acid, homocystine, cystathionine Failure of cellular cobalamin accumulation and/or retention with secondary failure of both methyl-cobsdamin and 5 -deoxyadenosyl-cobalamin synthesis 11.1... 

Patients typically present by 6-12 months with severe developmental retardation, convulsions, microcephaly and homocysteinemia (=50pmol/l) with hypomethioninemia (<20 pmol/1). A few individuals have had psychiatric disturbances. The blood concentration of vitamin B12 is normal, and, unlike individuals with defects of cobalamin metabolism, these patients manifest neither anemia nor methylmalonic aciduria. The blood folic acid level is usually low. 

C (ascorbic acid) 5 -Deoxyadenosyl cobalamin Transfer of methyl groups intramolecular rearrangements Antioxidant Anemia, pernicious anemia, methylmalonic acidosis Scurvy (swollen and bleeding gums, subdermal hemorrhages)... 

The methylmalonic acidemias [14, 15] are a family of disorders in the metaboUsm of branched-chain amino acids in which the activity of methyl-malonyl-CoA mutase is defective. They may be divided into mutase apoen-zyme defects and defects in cofactor synthesis or cobalamin metabolism. 

Type III Methylmalonic, methylcitric and 3-hydroxypropionic acids Primary failure of 5 -deoxyadenosyl-11.2 cobalamin synthesis ... 

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